Different systems and methods for changing the natural colour of hair are known in the art. These systems and methods involve the use of hair colouring compositions which allow either permanent or temporary change of hair colour. Hair colouring compositions which are used to permanently change the colour of hair, also called oxidative hair colouring compositions, typically comprise oxidative hair dye precursors, which can diffuse into the hair through the cuticle and into the cortex where they then react with each other and with a suitable oxidizing agent to form the end dye molecules. Due to their larger size, the resultant molecules are unable to readily diffuse out of the hair during subsequent washing with water and/or detergents; hence delivering a consumer-desired permanency of colour. This reaction typically takes place at approximately pH 10 to 11 in the presence of an alkalizing agent and an oxidizing agent. Typically an oxidizing composition (also called developer and/or oxidizing component) comprising the oxidizing agent and a dye composition (also called tint or dye component) comprising the alkalizing agent and if present the hair dye precursors are mixed shortly before use. The consumer repeats this process regularly in order to maintain the desired hair colour, shade and intensity of colour and to ensure continual, even coverage of the hair including coverage of new hair growth. The problem with standard oxidative hair colouring methods is that the conditions under which the reaction is taking place, i.e. the high pH value as well as the presence of an oxidizing agent may cause damage to the structure of the hair and may be irritating for the scalp of the user, especially when such a process is repeated regularly and the compositions which are usually used have an undesirable odour. Furthermore, obtaining the desired colour result is not easy since standard oxidative hair colouring compositions are reactive compositions and it is therefore not easy to control the reaction on hair.
Alternatively, systems and methods for temporarily changing the colour of hair have also been developed. These systems and methods usually involve the application of hair colouring compositions comprising direct dyes. Direct dye compositions are usually less aggressive for the hair in that they are non reactive compositions. However, the problem with these compositions is that the hair colouration which is obtained is typically characterized by a weaker washfastness than when the hair is coloured with standard oxidative hair colouring compositions, especially when the hair is washed with standard shampoo compositions. A further problem with direct dyes is that since direct dyes are low molecular weight molecules, they may have the tendency to also colour the scalp of the user.
Therefore, there is still the need for a hair colouring formulation and a method for providing the hair with the desired colour result and colour intensity in an easy manner. There is also the need for a hair colouring formulation and a method providing a hair colouration which is characterized by a better stability and good washfastness. Furthermore, there is also the need for a hair colouring formulation and a method involving the use of hair colouring compositions which are less aggressive for the hair and for the scalp. Finally, there is also the need for a hair colouring formulation and a method using compositions which are less smelly.